Communicators, Active Processes#
Communicator management is repeated in every “select MY_COMM
” step.
If it exists, the previous communicator is freed. When you run Q<=P
processes, the first Q
ranks of MPI_COMM_WORLD
are put into one
group, and the remaining P-Q
get MPI_COMM_NULL
.
The group of MY_COMM
calls the active processes group.